So-called "robotic" machines are coming into use for a wide variety of applications. Robotic agricultural machines, underground mining machines and floor cleaning machines have received recent publicity. The techniques used to guide robotic machines are nearly as varied as the machines themselves. Examples of such techniques include scanning beam navigation with remotely-mounted "targets" such as reflectors or bar codes, inertial navigation using ring laser gyroscopes, multi-beacon triangulation and others.
The patent literature depicts a variety of techniques for machine guidance. For example, U.S. Pat. No. 4,939,522 (Newstead et al.) involves a method and system for monitoring vehicle location. Such system uses two or more sweeping transmitters, the signal from each having a null in the signal wavefront. The system shown in U.S. Pat. No. 3,680,121 (Anderson et al.) uses pulses of modulated RF energy emitted from a vehicle. Multiple receiving stations compare the time of receipt of a pulse with a standard reference signal to compute the distance between the vehicle and the receiving station.
While the apparatus of U.S. Pat. No. 4,012,588 (Davis et al.) is used to determine position of a stylus (rather than guide a machine), the technique is of some interest. The stylus periodically emits a sound signal detected by two beacons. The signal transit time is measured to compute the stylus coordinates. In the alternative, the beacons emit sound waves detected by the stylus and the transit times of such sound waves are computed. The apparatus of U.S. Pat. No. 4,758,691 (DeBruyne) operates in a similar manner.
Although not involving machine guidance, the "determinator" shown in U.S. Pat. No. 2,434,644 (Fairweather) is interesting in the way it locates a source of acoustic shock waves. The time at which such wave arrives at each of two microphones is used to compute the angle between a reference axis and a radian pointing in the direction of the source.
And styluses and radio-frequency transmitters are not the only types of devices used to transmit energy sound waves. U.S. Pat. No. 4,530,077 (Dorr) depicts a cone associated with a sound-producing transducer. A portion of the cone is covered with sound-absorbing material so that when the transducer is actuated, the sound wave propagated from the cone is "shaped."
While the prior art guidance systems have been generally satisfactory for their intended purposes, they are not without disadvantages. For example, guidance systems involving ring laser gyroscopes are undoubtedly too costly and too complex in operation and maintenance for use with machines costing a few thousand dollars and operated by non-technical persons.
A disadvantage of scanning systems involving remote targets, e.g., bar code "stickers" on walls, is that the area in which the machine is to operate must first be rather extensively prepared or "set up." Sometimes, such setup work involves taking and recording certain measurements. Other systems, e.g., that of the Newstead et al. patent mentioned above, contemplate that such systems will be used at a particular location or area and will not be moved from place to place.
A method and apparatus for guiding a machine which addresses and overcomes some of the aforementioned disadvantages would be an important advance in the art.